Method of temporarily sealing a permeable formation

ABSTRACT

A composition is provided which may be employed for the selective sealing of permeable formations. The composition contains at least one particulate galactomannan gum which has been treated to render the gum hydrophobic in aqueous solutions having a pH of at least about 7.5; a pH control agent, and a water-soluble organic polymeric suspending agent.

United States Patent 1191 Coulter, Jr. et a]. 1 Oct. 9, 1973 [54] METHOD OF TEMPORARILY SEALING A 3,198,268 8/1965 Lindblom et a1. 175 72 PERMEABLE FORMATION 3,227,212 l/l966 Black et a] 166/294 3,251,768 5/1966 Walker 252/85 1 Inventors: Albert Coulter, Jr-; D ni L- 3,319,715 5/1967 Parks 175 65 Gibson; Kenneth H. Nimerick, all of 3,421,584 1/1969 Eilers et a1.... 166/295 Tulsa, Okla, 3,500,929 3/1970 Eilers et al.... 166/295 3,615,794 10/1971 Nimerick 106/209 1 Asslsnefi The Chemical Company, 3,687,200 8/1972 ROUISOII 166/295 Midland, Mich.

[22] Filed: Apr. 3, 1972 Primary Examiner-Stephen J. Novosad 1 PP 240,791 Attorney-William M. Yates Related U.S. Application Data [63] Substitute for Ser. No. 113,089, Feb. 5, 1971, which is a continuation-inart of Ser. No. 67,675, Au 3, 1970, abandoned, which is a continuation of Ser. No. [571 ABSTRACT 623,232, March 15, 1967, abandoned.

A composition is provided which may be employed for [52] U.S. Cl. 166/294, 166/295 the selective sealing of permeable formations. The [51] Int. Cl E2lb 33/138 composition contains at least one particulate galacto- [58] Field of Search 166/295, 294; mannan gum which has been treated to render the 175/65; 252/855 A; 106/209 gum hydrophobic in aqueous solutions having a pH of at least about 7.5; a pH control agent, and a water- [56] References Cited soluble organic polymeric suspending agent.

UNITED STATES PATENTS \Vyant et al. 252/855 X 2 Claims, No Drawings METHOD OF TEMPORARILY SEALING A PERMEABLE FORMATION CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of application Ser. No. 113,089, filed Feb. 5, 1971, allowed, which in turn was a continuation-in-part of application Ser. No. 67,675, filed Aug. 3, 1970, now abandoned, which in turn was a continuation of application Ser. No. 623,232, filed Mar. 15, 1967, now abandoned.

BACKGROUND OF THE INVENTION It is often desirous to temporarily seal or plug a permeable formation such as those located in a subterranean formation penetrated by an opening, e.g. borehole, so that other less permeable zones can be treated (i.e. fractured, acidized, etc. Many methods and compositions have been employed for temporarily plugging or sealing these openings and passageways. Plugs and seals composed of various type materials are known and used. For example, fibrous, flaky or granular plugging agents, cement and viscous gels have been employed as plugging and sealing agents. These present methods and agents suffer from certain disadvantages. Fibrous materials, e.g. hay, sponges, etc., do not perform with predictable success and in many instances an impervious seal is not obtained in vuggs or fissures even when large quantities of material are pumped into the zone. Cementing requires an extended period of time both to allow the cement to set and then breaking through (drilling) the cement once circulation is again desired. Furthermore, cementing can be quite expensive and also can cause serious damage to producing formations. The more recent use of gels, such as crosslinked polysaccharides, has proved to be a great improvement over the former methods. However, difficulties found in the use of many of these gels include, instability ofthe gels with pH changes, nonuniformity of the gel solutions placed into the borehole, premature setting up (hydration and crosslinking) of the gels, a prolonged setting time, failure of the gel to break down within a certain predetermined period of time, high fluid loss of the unset gels, weaknessof the set gel to extrusion caused by pressures and low resistance to elevated temperatures. There is therefore a need for a composition that can be emplaced as a readily pumpable slurry, thereafter sets up to form a mass capable of withstanding appreciable pressure, and subsequently liquefies so that the plug ceases to restrict the flow of fluids through the formation.

The present composition demonstrates uniformity, strength, predictable gellation setting times and break down times, good fluid retaining characteristics, and stability to a wide range of pH values. The composition may be prepared at the site of use employing locally available water supplies having a wide divergence in initial pH values, e.g. 3 to 10.

As employed herein a readily pumpable slurry is a slurry having rheological properties such that it can be pumped through 100 feet of 2 inch inside diameter pipe at a minimum rate of about 2 bbls/minute with about 100 psi pumping pressure.

SUMMARY OF THE INVENTION The present invention comprises a granulated formulation; an aqueous slurry composition containing a portion of the constituents of the granulated formulation in solution, and a method of treating a permeable subterranean formation employing the slurry.

The granulated composition comprises a galactomannan gum which has been treated to render the gun hydrophobic (less hydrophillic than normal) when dispersed in an aqueous solution having a pH of at least about 7.5; a pH control agent, and a water-soluble organic polymer suspending agent.

To employ the composition, it is mixed with a sufficient amount of water (as a carrier liquid) to make a readily pumpable slurry mixture. The slightly viscous slurry is injected (such as by pumping under pressure) into the formation to be sealed where it autogenously gels, i.e. sets up, to give a temporary, fluid-tight, pressure resistant, rigid gel which subsequently (after a period of time) disintegrates and ceases to plug.

PREFERRED EMBODIMENTS OF THE INVENTION In the practice of the present invention, the granulated composition comprises the following combination of constituents as parts by weight.

Constituent Range Preferred Hydrophobic galactomannan gum 50-4500 300750 A readily water-soluble organic polymeric suspending agent 3-100 20-60 pH control agent 003-600 018-300 To make the novel slurry composition of the present invention, the granulated product (considered in pounds for illustrative purposes) is admixed with a sufficient quantity of an aqueous solution to make an equivalent of 1,000 gallons of slurry. An equivalent of about 50 pounds to about 2,200 pounds of the composition defined by column one or from about 300 to about 1,080 pounds of the preferred composition are admixed with a sufficient quantity of an aqueous solution to make about 1,000 gallons of the indicated slurry.

Galactomannan gum as employed herein refers to those natural occurring polysaccharides derived from various endosperms of seeds. They are primarily com posed of D-mannose and D-galactose units. They gen erally have similar physical properties, such as being soluble in water to form thick highly viscous solutions which usually can be gelled (cross-linked) by the addition of such inorganic salts as borax. Examples of galactomannan gums include Tara, I-Izizachi, locust bean, Paloverale, Flame tree, guar, Honey locust, Green garrafin, Kentucky coffee bean, Japanese pagoda, Prairiemimosa, Indigo, Jenna, Rattlehox, Lucerne, Clover,

Fenergruk seeds and Soy bean hulls. The gum is provided in a convenient particulate form generally smaller than what will be retained on a No. 20 mesh sieve (US. Standard Screen Series) but larger than that which passes through a No. 200 mesh sieve.

A hydrophobically treated galactomannan gum as employed herein is a galactomanrnan gum which has been treated in such a manner that the natural hydrophillic properties of the gum are inhibited sufficiently to allow the gum to be dispersed in an aqueous carrier liquid having a pH of about 7.5 or greater and the dispersion to be emplaced in a permeable zone before any substantial hydration (swelling or opening) of the gum occurs. The gum, however, swells in acidic solutions. The treating agent is herein referred to as a hydrophobing agent. To render the gum hydrophobic it may actually be pretreated to undergo some physical or chemical change prior to being placed in an aqueous carrier liquid (e.g., by being treated with a suitable hydrophobing agent) or it may be associated with (coated, admixed with, etc.) a hydrophobing agent which affects the normal hydrophillic characteristic of the gum after being placed into the carrier liquid.

The hydrophobing agent may be any material capable of temporarily inhibiting the natural hydrophillic property of the gum. An example of a hydrophobing agent which affects the hydrophillic characteristic of the gum after being placed in the water is a material capable of liberating borate ions when added to water, e.g. alkali metal borates, sodium tetraborate (borax), sodium perborate, and sodium metaborate are preferred agents for use in the practice of the present invention. Details of one method for pretreating the gums with such a hydrophobing agent is taught in U.S. Pat. No. 2,868,664. Generally, a sufficient amount of the boron containing agent is employed to bring the pH of an aqueous dispersion of the gum up to at least about 7.5. From about 0.5 to 1.0 per cent by weight of such agent, based on the weight of the gum, is usually sufficient. Preferred gums are guar, tara or locust bean treated with borate ion liberating material.

Further information is available on the subject of borate-treated galactomannan gums in Chemical Abstracts vol. 43, part 3, column 69360 of Sept.Nov., 1949 and in Industrial Gums by Whistler and BeMiller; published by the Academic Press, New York (1959), page 339.

As indicated the hydrophobically treated galatomannan gum hydrates very slowly in aqueous solutions having a neutral or alkaline pH but hydrates very quickly in acidic aqueous solutions.

The exact amount of gum employed for gel stability will depend to some extent on the temperature to which the set gel will be subjected in the formation to be sealed. At higher temperature levels, e.g. greater than about 125F, a greater amount of the gum should be present. For example, above l25F a gel composition containing guar gum, polyacrylamide and sodium dichromate at a total concentration of about 500 lbs/960gallons of water has been found to be satisfactory whereas a concentration of only about 300 lbs/980 gallons of water was found practical for use at temperatures ranging from about 60 to 125F.

The suspending agent comprises a watersoluble organic polymer which is readily dispersible in aqueous solutions having a neutral to alkaline pH, i.e. the initial pH of an aqueous dispersion of the slurry composition of the present invention, to form visually continuous solutions or dispersions.

The terminology water-soluble, organic polymer, as used herein refers to nonionic, anionic, cationic or ampholytic organic materials composed ofa number of repeating units or mers. The useful polymers are characterized by dispersibility in water to form visually continuous solutions or dispersions. This includes truly water-soluble polymers which disperse in water to provide homogeneous, transparent solutions subject to water dilution without phase separation. Also included within the meaning of water-soluble, as used herein, are the water-swellable polymers which readily disperse in water to provide a highly disperse and visually continuous system of individually distinct, gel particles.

The water-soluble, organic polymers useful herein are available in a wide variety of chemical composition.- They may be obtained as natural polymeric products, by modification of natural polymers or by synthesis from polymerizable materials.

Water solubility is imparted to such polymers by the presence in and along the polymer chain of a number of hydrophilic moieties sufficient to more than offset the otherwise hydrophobic character of the organic polymer. One class of such hydrophilic moieties includes the ionizable groups. Among these are the sulfate and sulfonate groups, carboxylate salt groups, amino and ammonium groups, the latter being inclusive of protonated as well as quarternary derivatives of the amines, e.g., mono-, diand trialkyl substituted ammonium salt groups, and phosphoric acid groups and monoand dibasic salts thereof. Whenever acid salts are referred to, those generally intended are the alkali metal, alkaline earth metal (water-soluble species thereof) and ammonium salts.

Another class of water-solubility imparting, hydrophilic moieties are such nonionizable groups as carboxamide and monoand dialkyl N-substituted carboxamides, having a total of up to about 8 carbons. Also of a hydrophilic nature, though less strongly than some of the aforementioned groups are hydroxyl, acetal, ketal, carbamate and lactam groups. In any event, the polymers employed herein contain one or more of the aforedescribed hydrophilic moieties, and the like, in and along the polymer chain in a sufficient amount to render the resulting polymer water-soluble as defined above.

The polymers used in the invention are characterized by a high molecular weight. An adequate molecular weight is shown if the polymer can be obtained as a particulate solid and a 2 per cent by weight solution of the polymer in water, at a pH of 7, has a viscosity measured with a Brookfield viscosimeter at 25C of at least 10 centipoises.

Technology for preparing the water-soluble polymers useful herein is known. Useful ethylenically polymerized polymers are described in Hedrick et al., U.S. Pat. No. 2,625,529, Aimone et al., U.S. Pat. No. 2,740,522 and Booth et al., U.S. Pat. No. 2,729,557. A variety of water-soluble polysaccharide derivatives are described in Gloor, U.S. Pat. No. 2,728,725. Water-soluble polyurethanes or chain extended polyols are taught in Honea et al, U.S. Pat. No. 3,054,778 and a variety of polycarbonates and polylactams in Hibbard et al., U.S. Pat. No. 3,044,982, Walles et al., U.S. Pat. No. 2,946,772, Vitales, U.S. Pat. No. 2,874,124 and Fong et al., U.S. Pat. No. 3,000,830. These are to mention but a few of the well-known chemical avenues for the preparation of water-soluble, macromolecules. Further general descriptions of a variety of water-soluble, particulate macromolecules is contained in Davidson and Sittig, Water-Soluble Resins," Reinhold Publishing Corp., New York, 1962.

Preferred for use herein are water-soluble carbamoyl polymers. The most common forms of these are ethylenically polymerized polymers having attached along their polyalkane backbone a plurality of carbamoyl groups according to the formula:

wherein R, and R are independently selected from the group of hydrogen and alkyl hydrocarbons with one to four carbons. I

In particular, useful carbamoyl polymers include the various water-soluble homopolymers and copolymers of acrylamide and methacrylamide. Other carbamoyl polymers are the various water-soluble copolymers of N-substituted acrylamides such as N-methyl acrylamide, N-propyl acrylamide and N-butyl acrylamide. Still other carbamoyl polymers are prepared from the amides and half amides of maleic and fumaric acids. In general, any ethylenically unsaturated and polymerizable monomer, which contains the carbamoyl group, may be employed in the preparation of the preferred carbamoyl polymers.

Best results are obtained, if at least about 25 mole per cent of the polymerized'mers have carbamoyl substituents. The balance of the comonomers used to prepare the copolymers can be provided in the form of any water-soluble, or water-insoluble, monoethylenically monomer copolymerizable therewith, so long as the total amount of water-soluble monomers used is sufficient to impart water-solubility to the finished polymer.

Other water-soluble polymers useful herein are the lightly cross-linked water-swellable polymers. Such cross-linking can be achieved by irradiation of linear, water-soluble polymers under conditions which promote cross-linking or by incorporating a small amount, e.g., up to 1 percent by weight, of a polyfunctional monomer into the polymerization recipe for a linear water-soluble polymer. Examples of such monomers, which may be co polymerized with monoethylenically unsaturated monomers, are methylenebisacrylamide;

divinylbenzene, divinylether, divinylether of ethylene glycol and the like.

It is usually preferred that the suspending agent forms a near neutral or basic pH value when dispersed in an aqueous solution, i.e. one which will not cause an acidic pH and thus cause a premature swelling of the hydrophobically treated gum.

As indicated, one type of polymer found to be especially effective for this purpose is acrylamide polymers, including specifically polyacrylamide in varying degrees of hydrolysis and acrylamide copolym erized with one or more ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, vinylsulfonic acid, vinylbenzylsulfonic acid, vinylbenzenesulfonic acid, and alkali and alkaline earth metal salts of such acids as described in US. Pat. No. 2,831,841, column 3, lines 34 to 45 and in U.S. Pat. No. 2,909,508, examples I to 5.

Preferably the acrylamide polymer and acrylamide copolymers are those having a molecular weight such that when dispersed in a neutral or alkaline solution in an amount ranging from about 0.05 to about 1 percent by weight give a viscosity ranging from about 5 to about 200 centipoises at ambient temperatures. Preferably the viscosity is achieved within about minutes.

A particularly good suspending agent to employ is a polymer of from about 40 to 60 vinylpyrrolidone and 60 to 40 acrylamide (molar proportions) copolymerized by mixing between about 0.5 and 1.0 per cent, by weight, of the monomeric mixture of a cross-linking agent, e.g. methylenebisacrylamide, in the presence of between about 0.1 and 0.5 per cent of a catalyst, e.g., azobisisobutyromitrile, in about a 10 to 40 percent aqueous dispersion.

Other water-soluble organic polymeric materials found effective are synthetic derivatives of cellulose and natural occurring water-soluble gums which are not affected by the presence of the hydrophobing agent and which produce a neutral to alkaline pH when dispersed in an aqueous solution, and modified starches having similar characteristics. Examples of natural gums which give a near neutral pH are the tree exudates including gum arabic, gum tragacanth, kutera gum, ghati, mesquite gum and the like. Cellulose derivatives which may be employed include, for example, methylcellulose, hydroxy propyl methylcellulose, cellulose ethers and esters, e.g., as set out in Encyclopedia of Chemical Technology, 2nd Ed., vol. 4, page 618, John Wiley and Sons, New York, .and other similar suspending agents. The exact agent employed is not critical to the practice of the invention except to the extent that it functions as defined hereinbefore.

Preferably the suspending agent is employed in an amount ranging from 0.05 to 10 per cent by weight of the galactomannan employed. The exact amount of suspending agent will depend on the amount of hydrophobically treated gum employed, the temperature at which the slurry is to be employed, the other constituents present in the slurry and the capacity of the injection equipment (e.g. pumps, blenders, etc.). The suspending agent allows for the formation of a slightly viscous slurry containing an even dispersion of the galactomannan gums therein and prevents fluid loss of the initial slurries so that the gumcan be emplaced into position in the permeable zone to be treated.

A pH control agent should be employed to maintain the pH of the initial slurry at least at about 7.5, preferably between about 8 and 12. This assures that the hydrophobically treated gum will not prematurely swell because of acidic conditions. A hydroxyl ion source and/or preferably a buffering agent may be employed.

The hydroxyl ion source may be any soluble or partially soluble hydroxide or carbonate that provides the desirable pH value in the slurry. C.a(OH) or Mg(OH) are preferred. Other acceptable materials are Bi(Ol-i Co(OH) Pb(OH) Ni(OH) Ba(OH) Sr(OH) and the alkali metal hydroxides and carbonates. The amount of the hydroxyl ion source to provide is that which is sufficient to yield a pH value in water of at least 7.5 and preferably between 8.0 andl2.

A buffering agent is preferably employed in the prac tice of the present invention to provide a buffered solution, i.e. a solution to which moderate amounts of either a strong base or acid may be added without causing any large change in pH value of the solution. A buffer solution usually contains a weak acid and a salt of the weak acid, an acid salt with a normal salt or a mixture of two acid salts. Examples of suitable buffering agents which may be employed to provide a buffered solution having the desired pH value are NaH PO Na HPO boric acid-sodium hydroxide; acetic acid-sodium hydroxide; boric acid-borax; sodium carbonate-sodium bicarbonate; and sodium bicarbonate, or other like agents. By employing :a buffering agent instead of merely a hydroxyl ion producing material a composition is provided which is more adapted to a wide variance of pH values found in local water supplies and the influence of acidic materials located in formations and the like. The pH control agent may be varied between about 0.6 percent and about 40 percent by weight of the treated gum employed.

The invention is not dependent upon a theory as to its operation. It is not presently known how the various components of the fluid composition function during the gelation stage. One theory is that the borate treated gum is crosslinked in aqueous solutions having a high pH thus minimizing its solubility and retarding its hydrolysis at a basic pH. At temperatures below 175F the strength of this crosslinking mechanism is sufficiently strong to prevent hydrolysis. Above 175F, sufficient energy is present to allow hydrolysis and subsequent increases in viscosity of the aqueous system. It is known that galactomannans as a class are degraded by both acidic conditions and by heating to temperatures above 150F. Most rapid degradation occurs when both high temperatures and an acidic pH (less than 7.0) are present. It has been found that as a galactomannan water system is heated to an elevated temperature, i.e. above about 150F, the pH of the solution decreases, becoming more acidic. it has been postulated that such decrease in pH is the result of degradation of the galactomannan to produce various organic acids. It is, therefore, one purpose of this invention to recognize the foregoing hypothesis as applicable and to use various metal hydroxides as a means of neutralizing these organic acids as they are formed or by using a buffering agent to provide buffered solution. By neutralizing said organic acids, or by providing a buffered solution the rate of degradation is retarded and the efficiency of the gum system is extended. Frequently, fluid loss control agents are advantageously employed in the invention. The preferred material is silica flour (particles having an average size of less than about 1 micron and more desirably less than 0.1 micron). However, any substantially inert organic or inorganic pulverulent material (including starches and the like) may be employed as the fluid-loss control additive.

All the particulate constituents of the invention can be premixed and packaged in a convenient form. When ready for use, the particulate product is simply admixed with the necessary quantity of an aqueous solution to form an aqueous slurry of the treated gum. The slurry is then pumped into the formation to be sealed whereupon it sets up to form a firm plug. The set plug will breakdown after a predetermined period of time, thus allowing circulation through the treated area.

Since the ingredients are readily dispersible, the composition of the invention is easily prepared. it exhibits excellent low fluid-loss, thickens at a controllable rate which may be a relatively short time, if desirable, e.g. between one-half hour and 1 hour, or over a period of several hours if preferred, and thereafter liquefies within a few hours or longer, as desired.

In the following Examples tests were conducted to show the desirable properties of the gelled composition of the invention. Thickening or gel time and plug life were determined for each series and are set out in the tables appearing hereinafter.

Thickening time, which herein is also considered the gel time, was determined according to Section 10, page et seq., of AH RP 108 (March, 1965), employing the schedule designated herein for each series of tests. The gel time is also referred to herein sometimes as working time because it is the permissible time between admixture of the ingredients and the gelation during which the composition remains fluid.

The time between gelation and breakdown or liquefaction of the gelled plug is called herein plug life. It was determined as follows:

A vertically held 34-inch diameter 6-inch long steel pipe nipple, capped at the lower end, and containing a %-lnCh diameter steel ball, was nearly filled (allowing a little room for expansion) with a quantity of the slurry gelable composition. A cap was placed on the top of the nipple and it, with its contents put vertically in a bath, which had been preheated to a specified temperature. Thereafter, at 15-minute intervals, the nipple was inverted, the ball falling freely through the ungelled fluid. The inverting process was continued through the gelation stage, at which time the ball became firmly in an immobile state by the gelled composition, and thereafter the periodic inversion further continued until the gel broke and again allowed the ball to fall freely. The sound of the ball striking the cap at the bottom of the nipple when inverted indicated that the gel had liquefied, and this was recorded as the plug life. The reliability of this test was also confirmed by opening the system and observing the state of the admixture.

The tests were conducted by admixing the particulated borated gum with the proper amount of water and thereafter adding a pH control agent, e.g. a soluble carbonate-or hydroxide, when used, followed by a suspending agent, e.g. an acrylamide polymer to the aqueous dispersion of gum.

EXAMPLE 1 500 Pounds of particulated hydrophobically-treated guar gum (prepared according to US. Pat. No. 2,868,664) were admixed with 50 pounds of linear polyacrylamide, about 30 percent hydrolyzed, (purchased under the trademark Separan NP30) and enough water to make 1,000 gallons at the ambient temperature of about F. One portion of the slurry composition so made was tested at 250F for working time (time elapsed between mixing and state of gel taken as poises) recorded in minutes according to the procedure of Schedule 19 of Section 10 of API RP 103. A second portion was tested for plug life as above described.

A series of tests (Nos. 2-6Table I) were conducted at a temperature of 250F and an increasing amount of soda ash (commercial grade Na CO was admixed with the borated guar gum prior to admixture of the polyacrylamide.

A second series of tests (Nos. 7 8t 8 Table I) were conducted at a temperature of 250F employing Ca(OH) instead of soda ash.

Test No. 9 Table I was conducted as in the second series except that the temperature of the test was 265F and the plug life was determined according to Schedule 20 of Section 10 of RP! RP 108.

In the next series of tests (Nos. 10-19), the tests were conducted according to the procedure followed in Test No. 9 except that the temperature of the test was 300F and either soda ash or Ca(OH) was admixed with the borated guar gum before admixing the polyacrylamide therewith.

In the final series of tests (Nos. 20 & 21) tests were conducted according to the procedure in the previous series except the temperature employed was 325F and the Schedule of Section 10 of API RP 10B followed was Schedule 21.

The results of these tests are shown in Table l.

TAB LE I 500 Pounds of Borated Guar Gum and 50 Pounds of Acrylamido Polymer per 1,000 Gallons of Dispersion Working Temperatime in Section 10 Additive in pounds p]! value ture of minutes AI'I RP 1011 per 1,000 gallons when test in to reach schedule Test number of coniposltion made up 1. 100 poisus followed Plug lltv None 8. G 250 48 it! 4.5 days. NazCOa 250 00 l.) 4.5 days. NDJCO: J. 3 250 125 it! 6.5 days. 30 NBzCO; 9. 8 250 290 10 7.0 days. 50 NazCO; 10. 1 %O 19 8.0 days. 80 NazCO; 10. 250 19 8.0 days. 5 Ca(OH)g 10. 0 250 100 10 5.5 days. 08(011): 250 300 19 8.0 days. Ca(OH)2 11. 7 265 185 20 8.5 days. 10 NazCO; 9. 3 300 40 21 23.5 hours. 40 NazCOa 300 21 28.5 hours. 50 N21200: 10. 1 300 130 .21 20.0 hours. 100 NazCOa 10. 4 300 160 21 24.0 hours. 250 NBzCOa 10. 5 300 190 21 20.0 hours 400 N 82003 10. 5 300 150 21 64.0 hours 40 Ca(OH)z 300 21 32 hours 75 Ca(0H)z 11.8 300 120 21 74 hours Ca(OH)z 11. 9 300 21 78 hours Ca(OH)z 12. 0 300 105 21 85 hours 160 Ca(0H)z 12.0 325 80 21 9 hours. 250 Ca(OH)z 12. 4 300 75 21 10 hours.

EXAMPLE 2 length of time for dissolution or disintegration (gel- In this example, tests were conducted similarly to those in Example 1 except that 750 pounds of a borated galactomannan gum (as exemplified by borated guar gum) were used and the temperature of each test was increased by 25 Fahrenheit degrees as shown in Table II. The resulted working time and plug life tests are also shown in Table II.

TABLE 11 750 pounds of borated guar gum and 50 pounds of polyacrylamide per 1,000 gailons of dispersion Working Reference to Tables I and 11 shows that a high temperature plug can be made at temperatures from l75F to 325F, employing a borated galactomannan gum and a polyacrylamide polymer. it can be seen that the higher the temperature, the faster the composition gels. However, it is shown that the rate of gel can be retarded by the use of such alkaline materials as sodium carbonate and Ca(OH) The Tables also show that as little as 25 pounds of an acrylamide polymer both suspends the borated galactomannan gum and also imparts a moderate increase in pH value to provide an adequate working time within a temperature range of between about l75F and about 200F. At above about 225, the acrylamide polymer concentration is best increased to at least about 50 pounds per 1,000 gallons of composition. It is preferable that the amount be increased to about 75 pounds, per L000 gallons of gelable composition, at temperatures approaching 300F and above.

The degeneration or dissolution of the plug after emplacement occurs over a predetermined period of time. The higher the ambient temperature of the emplaced plug, the more rapid the degeneration of the plug. For example, a composition comprising 500 pounds of the borated guar gum and 50 pounds of the polyacrylamide polymer, the following conditions obtain: at F, it remains solid up to about 28 days; at about 225F for about 16 days; at about 250F for about 5 days. This breaking) of the plug is usually longer than is desirable. Therefore, less alkaline material, e.g. Ca(0l-l) or Na CO is admixed therewith to delay the gel-breaking period.

It is shown in the tables also that, at temperatures above about 250F, the working time of the aqueous suspension of the borated galactomannan gum containing the acrylamide polymer in the absence of the alkaline material to raise the pH value, is too short for common use. It is shown, however, that the addition of Ca(OH), or Na CO lengthens the working time. Ac cordingly, the addition of such alkaline materials provide the attainment of both objectives: an increased working time and lengthened plug life, as desired.

it is also shown that plug life, above a temperature of about 275F, may be increased by increasing the borated galactomannan gum employed, say on the order of about 750 pounds thereof per 11,000 gallons of aqueous composition being prepared.

EXAMPLE 3 In this example tests were conducted to show the effect of increasing the concentration of borated galactomannan gum in water and of admixing therewith varying amounts of Ca(OH) The procedure followed was to slurry the borated gum, herein borated guar gum, in the amount given in Table lll below, with the amount of water necessary to give the desired concentration, admix therewith the Ca(OH) when employed, and thereafter admix 25 pounds ofa suspending agent comprising polyacrylamide (about 30 percent hydrolyzed) and having an average molecular weight of between 2 and 3 million, known commercially as under the trademark Separan AP 30. The slurry so made was then placed in tubes and immersed in an oil bath, which had been preheated to 225F. The composition was observed to gel and then further observed so as to determine the time which elapsed before the gel broke. It was considered broken, when the viscosity dropped to under 10 poises.

The results are shown in Table ll].

TABLE III Pounds of Pounds of Borated Guar CatOi-i) added Plug Test Gum per 1,000 gallons per L000 gallons Lii'c Number of Composition of composition in Days 25 i None 3 26 50 1.0 7 45 Cd(OH) 9.05 54 27 50 5.0 10 46 Pb(OH), 9.1 72 28 50 10.0 15 47 Ni H) 9.0 54 29 100 None 48 Ba(OH) 11.9 56 30 100 1.0 7 49 Sr(OH) 9.05 54 31 100 5.0 ll 32 100 10.0 l7 5 33 200 None Reference to Table IV shows that various metal hy- 34 200 droxides extend the life of the plug composition of the .15 200 5.0 24 36 200 invention when admixed with the borated gum and the 37 300 N ne 14 thickening agent is thereafter admixed therewith. as 300 1.0 23 39 300 5.0 30 [0 EXAMPLE 5 Reference to Table m Shows the,t the plug life is This series of tests was run to show the use ofa cellulengthened as the amount of borated gum is increased. loste denvatllfe hydroxy! Ethyl CeHUIQSe a thick it also shows that the plug life is increased by raising the enmg agent m the compcfsmon of h T pH value of the slurry by admixing therewith an l5 procedure followed consisted essentially of admixing droxyl ion Source, fig" a Soluble hydroxide the amount of hydroxyl ion source, VIZ. Na CO or Ca- (OH) with water and therefor admixing the amount of EXAMPLE 4 hydroxy ethyl cellulose (abbreviated HEC) set out in A further series of tests was conducted to illustrate T m V l P of the freshly P P f compo some alkaline materials that may be used in the prao 20 sition, the time 1n minutes for the composition to reach tice of the invention to delay the gelation rate and reloo'pPlse "scoslty taken as the gel Polm) and the tard the rate of degradation or degeneration of the plug plug hfe are Set out m-Table TABLE v Pounds of borated guar gum Working per 1,000 Pounds of time in Temperagallons of HEC/1,000 Pounds of retarder pH value 2 minutes to ture composigallons of per 1,000 gallons when reach 100 Test number in F. tion composition of composition made poise Plug life 200 300 50 None 7.5-8 a0 10 days. 250 300 50 250 300 50 250 300 50 250 500 50 275 300 50 275 500 s 275 500 50 275 500 50 275 500 50 300 500 None 300 500 None 40 Ca(OH 2 105 20 hours. 300 500 50 45 Ca(OH)2 11.5 107 26 hours.

l Squeeze Schedule No. 19 API RP 10B applicable at 250 F. Squeeze Schedule No. 20 API RP 10B applicable at 275 F. Squeeze Schedule No. 21 API RP 10B applicable at 300 F.

1 pH values were determined by Hydrion pHpaper.

back to a fluid. The procedure followed was to admix the metal hydroxide with water in the proportion of 75 pounds of hydroxide per 1,000 gallons of composition; admixing borated guar gum with the aqueous hydroxide solution in a proportion of 500 pounds of the gum per 1,000 gallons of composition; and then admixing an acrylamide polymer (same as employed in Example 3) in an amount of 50 pounds per 1,000 gallons of composition. The mixture was then transferred to %-inch diameter, 6-inch long steel nipples each containing a -inch ball. Thereafter the nipples, as in the plug life tests above, were capped on both ends and placed in an oil bath, previously heated to 275F. The nipples were thereafter periodically inverted as above described when the composition was gelled, the ball became immobile. When the gel later broke, (the break point being considered occurring at a viscosity less than 50 poises) the ball fell with a clearly audible impact to the bottom of the nipple when inverted.

Table IV sets out the results.

TABLE IV Test Metal Hydroxide pH Value Plug Life Number Employed as Made in Hours None 8.6 48 41 Ca(OH), [2.0 [20 42 Mg(0H) 9.1 60 43 Na(OH) 12.0 86 44 Bi(OH), 9.05 54 EXAMPLE 6 This series of tests was conducted to show the low fluid loss to a porous earthen formation from the composition of the invention, prior to gel, by admixture therewith of a copolymer of percent N-vinyl-Z- pyrrolidone and 40 percent acrylamide, crosslinked with 0.7 percent N,N-methylenebisacrylamide, identified in Table VI as polymer J.

The tests were performed according to the standard Baroid Cell test employing l-inch diameter, l-inch long Berea sandstone cores (first saturated with 3 percent by weight aqueous CaCl employing a pressure of 1000 psi and the temperature designated in Table VI. The amount of borated guar gum employed in each test was that sufficient to provide 500 pounds per 1,000 gallons of composition. The amount of polyacrylamide suspending agent and hydroxyl ion source are shown in Table VI. The fluid loss in minutes and the total volume of liquid composition through the core are also set out in Table Vl.

TABLE VI Ingredients per 1,000 gallons of aqueous composition 4 Total volume J 1 fluid Perme- Fluid loss in ml. afterin mi. through Polyloss ability Temcell corrected Test acrylacontrol Added hydroxyl to air perature, 1 4 9 16 25 180 for 23.5 cm. Number mide polymer lon source in md. F. min. min. min. min min. min. area 25 None None 578 175 15. 5 28. 5 38. Out of fluid 25 667 175 10. 0 19. 27. 0 31 35 36 158. 4 25 675 200 18 22 24 24. 5 25 1 25 680 200 5 10 12.5 13 13. 5 15 66. 0 50 590 225 8 18 19. 0 19 19 19 83. 6 50 16 d 642 225 5 7 7 7 7. 5 8. 0 35. 2 50 None 5 lbs. of Na CO 635 250 10 15 20 22 24 24 105. 6 50 16 do 635 250 5 9. 5 12. 5 14 14 16 70. 4 50 None 75 lbs. of Ca(OH) 632 275 3 4 5 6. 1 6i. 2 9. 8 43. 1

1 .I polymer is 60% vinyl pyrrolidone and 40% aerylamide copolyrnerized with 0.7% N,N-methylenebisacrylamide as a cross-linking agent.

Reference to Table VI shows that fluid loss from the ungelled composition is greatly lessened by the presence of the specific vinylpyrrolidone-acrylamide crosslinked with methylenebisacrylamide in the amounts shown.

EXAMPLE 7 it is sometimes desirable that the gelled composition. be extruded as, for example, in treating formations comprising vugs and impacked fractures. in such instances, it is desirable that the plug resist up to about smaller openings and passageways where entrance of the treating fluid is desired.

it can be seen that the composition of the invention offers the advantages of providing a temporary plug particularly adaptable for use in porous earthen formations, which is fluid when made, can be readily emplaced as needed, then gels to form a plug of temporary nature which is excellent for diverting subsequently injected fluids, and which at high pressures can be forced into relatively larger opening farther removed from the entrance, and thereafter disintegrates to a fluid which can be easily removed and does no formation damage.

What is claimed is: t

1. A method for temporarily plugging a permeable formation which has an ambient temperature of at least about 150F located adjacent to a well bore which penetrates a geologic formation which comprises: admixing from about an equivalent of to about 2,200 pounds of the composition consisting essentially of, as parts by weight,

TABLE VII Pounds of colic hene fie e per 1,000 gallons Hydraulic Extrusion through pipe having diameter of-- of com- Temp pressure Test Number position in p.s.i. inch inch inch None 225 20 Rapid 1 inch in 10 5%.. No movement. 1 None 225 50 0. None 226 100 1 inch in 30 sec. 26 225 20 Rapid-.- 1 inch in 10 see.- No movement. 25 226 100 D 25 225 100 225 100 225 100 225 A 12-inch long, 2-inch diameter pipe nipple was equipped with caps. The lower cap contained threaded X1- and /4-inch diameter openings. The openings which were not being tested were plugged.

The gelable composition of the invention consisted essentially of borated guar gum, polyacrylamide (average weight between about 1,000,000 and 3,000,000) and water to make proportions of 500 pounds of the gum and 50 pounds of the polyacrylamide per 1,000 gallons of water.

The composition was poured into the l2inch by 2- inch pipe and subjected to an advanced temperature for a period of 20 hours and at the pressure shown in the Table VI]. Cellophane flake was added in the tests, as shown in the table, as a fluid loss additament.

Reference to Table Vllshows that the gelled compolarger opening and passageways as in an earthen forma- .sition of the invention can be readily extruded into the' tion being treated, e.g. fractured, where entrance of ex cessive amounts of the treating fluid into the larger openings is undesired, but will not so readily enter the a. from about 50 to about 1,500 parts of a particulate hydrophobically treated galactomannan gum so that when dispersed in an aqueous solution having a neutral to alkaline pH the gum does not readily hydrate in its normal length of time;

b. from about 3 to about parts of a readily watersoluble organic polymeric suspending agent, the suspending action of which is not effected by the hydrophobing agent; and V g,

. 0.03 to about 600 parts of a pH control agent in an amount which is effective to provide an initial pH in an aqueous solution in which the granulated composition is dispersed of at least about 7.5, with a sufficient quantity of an aqueous solution to make 1,000 gallons of a slurry and injecting the slurry into the permeable formation prior to any substantial hydration and cross-linking of the treated galactomannan gum occurs, and allowing the galactomannan gum to hydrate and cross-link while in saidpermeable formation.

15 16 2. A method for temporarily plugging a permeable mal hydrophillic characteristic in aqueous solution formation located adjacent to a well bore located in a having an acidic pH value; subterranean formation which comprises: injecting into b, a water-soluble organic polymeric suspending said formation prior to any substantial hydration of the agent, said water-solubility of said suspending treated galactomannan gum aslurry composition which agent not being effected by said hydrophobing comprises: agent and said agent producing about a neutral to a. from about 150 to about 1,500 pounds of a particalkaline pH value when dispersed in an aqueous soulate galactomannan gum which has been treated lution from about 3 to about 100 pounds; and with an effective amount of a hydrophobing agent c. a sufficient amount of an aqueous solution to make so that the gum is less hydrophillic than normal 1,000 gallons of said slurry, said solution being when dispersed in an aqueous solution having buffered to have an initial pH of at least about 7.5. about a neutral to alkaline pH value and has 8. nor- UNI' I'ED STATES PATENT OFFICE Q CERTIFICATE OF CORRECTION mm 3,763,934 Dated October 9, 1973 mo yA; W. Coulter, Jr., D. L. Gibson & K. H. Nimerick It is certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

e -1 YColumn 2, line 5, delete "gun" and insertt-gum--.

Column 5, line 66, delete "azo bisisobutyroflxitrile" and insert -azobisisobutyronitrile-.

Celumn 9, Table I, 5th column, last item, delete "300" and insert -325'.

yCelumn 13, line .31, delete one-sixteenth" and insert one-sixth".

Signed and sealed this 23rd dey of July 1974.

, (SEAL) Attest MCCOY 1 I. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. A method for temporarily plugging a permeable formation located adjacent to a well bore located in a subterranean formation which comprises: injecting into said formation prior to any substantial hydration of the treated galactomannan gum a slurry composition which comprises: a. from about 150 to about 1,500 pounds of a particulate galactomannan gum which has been treated with an effective amount of a hydrophobing agent so that the gum is less hydrophillic than normal when dispersed in an aqueous solution having about a neutral to alkaline pH value and has a normal hydrophillic characteristic in aqueous solution having an acidic pH value; b. a water-soluble organic polymeric suspending agent, said water-solubility of said suspending agent not being effected by said hydrophobing agent and said agent producing about a nEutral to alkaline pH value when dispersed in an aqueous solution from about 3 to about 100 pounds; and c. a sufficient amount of an aqueous solution to make 1,000 gallons of said slurry, said solution being buffered to have an initial pH of at least about 7.5. 